The present invention relates to a mobile communication resource assigning method and, more particularly, to a method of assigning resources such as soft hand-over processing mechanisms in the speech processing mechanisms of a mobile communication system, e.g., vocoders (VOICE CODERS) and CDMA (Code Division Multiple Access).
In a mobile communication system, in order to effectively use radio resources, speech codes of a low bit rate are used, and voice codecs, i.e., vocoders, are required.
In a mobile communication system using TDMA (Time Division Multiple Access), in order to increase the utilization efficiency of the transmission path between each base station and the center station, vocoders are arranged in the center station in one-to-one correspondence with radio channels on transmission paths, and time division multiplexing is performed between a plurality of channels of a low bit rate.
In a conventional scheme, these vocoders are generally prepared in number corresponding to the number of channels in radio base stations. For this reason, the number of vocoders required is equal to or larger than the number corresponding to the communication traffic, resulting in an increase in cost.
In a system which performs soft hand-over for speech frames as in CDMA, a soft hand-over processing mechanism for performing selective synthesis between a plurality of speech frames is required. Note that in a CDMA scheme, soft hand-over indicates that a mobile radio telephone moving from one cell area to another cell area is simultaneously communicating with the two cells through the same radio channel. In this case, in soft hand-over processing, redundant communication data received by one mobile telephone from two cells must be transmitted to a common call processing point in the system upon selecting a communication path, one of the communication data must be selected in real time while the other communication data is discarded, the reply must be copied to be sent to the two cells upon selecting communication paths, and the operations of the two cells must be harmonized with each other to simultaneously transmit the redundant replies to the mobile telephone.
In addition, a speech frame having a frame length of a variable rate is used in accordance with a speech state. For example, QCELP used by IS-95 of the TIA (Telecommunication Industry Association) standards is available.
Such a CDMA system uses a resources sharing method of performing transmission between each base station and the center station according to a frame relay scheme, and allowing an arbitrary relationship to be set between radio channels, vocoders, and hand-over mechanisms, as disclosed in U.S. Pat Nos. 5,305,308, 5,195,090, 5,278,892, 5,195,091, and 5,184,347.
When the frame relay scheme or ATM (Asynchronous Transfer Mode) is used to perform transmission at a low bit rate, the ratio of additional information such as a header to actual speech information increases, resulting in a deterioration in efficiency in the transmission path.
In order to solve this problem, a composite cell scheme of multiplexing a plurality of speech frames on one ATM cell has been proposed, as in ITU/SG-13 (ITU-T/SG-13, D899 and D900, July 1995).
As described above, in the above conventional scheme, the following problems are posed.
The first problem is that when speech frames are to be transmitted between each base station and the center station according to the packet scheme, the transmission delay varies. When transmission is performed by time division multiplex as in a TDMA system, once a multiplexing point is set, almost no delay occurs during communication. When transmission is performed by the packet scheme, queues and processing mechanisms therefor are present at various positions in the transmission system, the transmission delay changes with a change in transmission amount.
The second problem is associated with the performance of a soft hand-over mechanism. Whether selective synthesis of some soft hand-over processes can be performed within a predetermined processing delay value depends on the performance of each processing mechanism itself and leveling of processing requests.